JP3285157B2 - Phase information observation method and phase information observation interferometer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for observing phase information, and more particularly, to a method and an apparatus for observing phase information using a wave, such as an electron beam, whose amplitude is difficult to divide.

[0002]

2. Description of the Related Art Conventionally, electron beam holography is known for observing an image of a very fine phase object. The principle will be briefly described. In FIG. 3, a sample 2 is arranged on one side of the optical axis, and a highly coherent plane electron wave 1 is incident along the optical axis. The electron wave 1 transmits through the sample 2, is wavefront divided into an object wave modulated by the sample 2 and a reference wave that does not pass through the sample 2, is once collected by the electronic objective lens 3, and is formed on the intermediate image plane 5. An image is formed, and an electronic biprism 4 is arranged between the objective lens 3 and the image plane 5, and an object wave passing through one side of the central filament and a reference wave passing through the other side are bent so as to intersect the optical axis. Then, they are superposed on the image plane 5 to form interference fringes. The interference fringes are magnified by an electronic lens 6 and recorded on a photographic film 7 to form a hologram 7. In the hologram 7 created in this manner, the phase of the object wave spatially enlarged by the electron lens is recorded as a positional shift of the interference fringe. The phase of the recorded object wave can be measured by optically reconstructing the hologram 7 and causing the reconstructed wavefront to interfere with, for example, a plane wave. The measured data can be converted and calculated by calculation.

[0003] Further, as shown in FIG.
Using 1, 12, and 13, the incident electron beam 1 is diffracted by the crystal 11 and is amplitude-divided into a + 1st-order diffraction wave and a -1st-order diffraction wave. Respectively, so that one of the diffracted waves impinges on the sample 2 and the other impinges on the crystal 13 through the vacuum, and is diffracted again into the -1 and +1 orders, respectively. It has also been proposed to form an electron beam hologram by forming a hologram by overlapping and interfering with an observation surface 15 via an electron lens 14.

[0004]

Although electron beam holography by the wavefront division method shown in FIG. 3 is widely used, it has some problems. That is, since the interference fringe pattern itself does not directly represent the isophase distribution of the sample, it is necessary to reproduce the phase distribution of the sample from the interference fringe pattern optically or by calculation. In addition, a high coherence electron beam source is required for splitting the wavefront. In addition, a vacuum area for passing the reference wave is required immediately next to the sample area to be observed.However, there are few actual samples whose contours are clear like this, and there are only samples that can perform ideal measurement. Few.

[0005] The amplitude division method shown in FIG. 4 is hardly practically used because it is difficult to obtain a pure crystal that works as theoretically as shown in the figure, and it is very difficult to align its orientation.

SUMMARY OF THE INVENTION The present invention has been made in view of such circumstances, and has as its object to provide a phase information observing method and an interferometer for observing phase information using an electron beam or the like whose amplitude is difficult to be divided by a half mirror or the like. It is to be.

[0007]

According to the phase information observation method of the present invention which achieves the above object, two scattering films for randomly scattering incident waves are arranged in a conjugate manner, and between the two scattering films. A sample is arranged, a first interference pattern due to waves passing through both scattering films is detected, a second interference pattern is detected in the same detection state where the sample is removed, and the difference between the detected two interference patterns is calculated. Alternatively, the method is characterized in that phase information of the sample is observed as interference fringes by taking a product. In this case, it is desirable that the sample arrangement position is a position where the component going straight on the incident side scattering film is narrowed down, and that both interference pattern detection positions are conjugate to the sample arrangement position. Further, the interferometer for observing phase information of the present invention is an interferometer capable of observing the phase information of a sample as interference fringes. A lens system that is placed in between and forms an image of one scattering film on the other scattering film, and a sample that is disposed at a position where a component that goes straight through one scattering film is narrowed down by the lens system or a sub-system thereof. And a device for recording an interference pattern formed on the observation surface. When the incident wave is an electron beam, it is desirable to use an amorphous film as the scattering film.

[0008]

According to the present invention, two scattering films for randomly scattering incident waves are arranged conjugately, a sample is arranged between the two scattering films, and the first wave caused by the wave passing through both scattering films is arranged. The same interference pattern is detected, the second interference pattern is detected in the same detection state with the sample removed, and the difference, the sum or the product of the two detected interference patterns is taken, so that the equiphase fringe of the sample is directly observed. it can.

[0009]

In the present invention, two scattering films are used, one of which divides an incident wave into an object wave and a reference wave, and the other overlaps the two waves (the object wave and the reference wave) again. A random interference pattern modulated with a random phase distribution appears on the observation surface and is recorded, and the random interference pattern recorded with the sample inserted and the random interference pattern recorded with the sample removed are recorded. By detecting the random interference pattern and calculating the difference, sum or product of the two random interference patterns, the equiphase fringes of the sample can be directly observed.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A phase information observing method and a phase information observing interferometer according to the present invention will be described below with reference to the drawings.
Even now, an electronic biprism is indispensable for producing an electron beam interference fringe. However, in the present invention, it is considered that interference fringes are formed using two amorphous films without using the electronic biprism. Part 1
The electron beam is divided into an object wave and a reference wave by one sheet.
The sheet superimposes the two waves (the object wave and the reference wave) again and causes interference. That is, the object wave is a component that is scattered by the first amorphous film and then passes through the second amorphous film, and the reference wave is a component that the incident beam passes through the first amorphous film and then passes through the second amorphous film. This is the component that is scattered. By holding the lens and the sample at an appropriate position between the first amorphous film and the second amorphous film, the equiphase fringes of the sample can be directly observed.

The principle of the present invention will be described below with reference to the drawings. In FIG. 1, an amorphous film A is used as a scattering film.
1, an electron lens B1 is arranged at a position behind a distance f of the amorphous film A1 by using these and three electron lenses B1, B2, and B3 having a focal length f, as shown in FIG. The sample 2 is placed on the focal plane, the electron lens B2 is placed at a position behind the sample at a distance f, and the amorphous film A2 is placed on the rear focal plane. Then, an electron lens B3 is arranged at a position behind the amorphous film A2 at a distance f,
The rear focal plane of the electron lens B3 is defined as an observation plane C. Therefore, the amorphous films A1 and A2 are conjugate with each other,
The observation plane C is an imaging plane of the sample 2.

In such an arrangement, a component in which the incident electron beam 1 enters the amorphous film A1 and travels straight without being scattered by the film A1 converges to one point (reference point) on the sample surface by the electron lens B1. Then, it diverges again with the phase of this point, is converted into a plane wave by the electron lens B2, reaches the amorphous film A2 on the image plane of the amorphous film A1, is scattered in all directions there, and is sampled by the electron lens B3. The image is collected on an observation plane C, which is an image plane of No. 2. This component becomes a reference wave. Also, the light enters the amorphous film A1,
The component scattered in all directions by the film A1 is an electron lens B
1 collects on the sample surface and reaches the electron lens B2 with the phase distribution information of the sample 2, where the amorphous film A
Then, the light converges on the observation surface C, which is the image plane of the sample 2, through the film A2 and the electron lens B3. This component becomes an object wave. In addition, both amorphous films A1, A
There is also a component that goes straight through 2, and converges to one point on the observation plane C as shown by the solid line in the figure. Further, some components are scattered by both of the amorphous films A1 and A2, but the intensity is weak and can be ignored.

The above-mentioned reference wave and object wave interfere with each other on the observation plane C, and the phase difference of each sample point with respect to the phase of the reference point is modulated by a random phase distribution generated by the amorphous films A1 and A2. The pattern appears on observation plane C and is recorded.

Next, the sample 2 is removed from the irradiation beam (after the dynamic change of the sample 2 is observed),
An interference pattern having no phase information of the sample 2, that is, a random interference pattern of only a random phase distribution generated by the amorphous films A1 and A2 is recorded under the same conditions as above, and a random interference pattern when the sample 2 is in the irradiation beam is recorded. When a difference, a sum, or a product from the interference pattern is calculated, the result is an interference pattern representing an equal phase distribution of the sample 2.

[0015] This point will be briefly described using mathematical expressions.
The change in the wavefront due to the amorphous film A1 is expressed as exp (iφ ₁ ) ≒ 1 + iφ ₁
φ ₁ ≪1) The change in the wavefront due to the amorphous film A2 is expressed as exp (iφ ₂ ) ≒ 1 + iφ ₂ (when thin, ie,
φ ₂ ≪1) The change in wavefront due to sample _{2 is} expressed as exp (iφ ₀ ). Here, φ ₀ , φ ₁ , and φ ₂ are functions of coordinates (x, y) perpendicular to the optical axis. Further, the Fourier transform is represented by F, and F [φ ₁ ] = a ₁ exp (iα ₁ ) F [φ ₂ ] = a ₂ exp (iα ₂ ) F [exp (iφ ₀ )] = φ

Assuming that the incident electron beam 1 is 1, immediately after the surface of the amorphous film A1, 1 + iφ ₁ immediately before the second surface of the sample, δ + ia ₁ exp (iα ₁ ) immediately after the second surface of the sample, δexp (iφ ₀ (0, 0)) ) + Ia ₁ exp (i
α ₁ ) · exp (iφ ₀ ) exp (iφ ₀ (0,0)) + iφ ₁ * φ immediately before the surface of the amorphous film A2 ｛exp (iφ ₀ (0,0)) immediately after the surface of the amorphous film A2 + Iφ ₁ * φ｝ ・ (1+
iφ ₂ ) On the observation plane C (wave function), ｛δexp (iφ ₀ (0,0)) + ia ₁ exp (iα
₁ ) · exp (iφ ₀ )｝ * {δ + ia ₂ exp (iα ₂ )} = δexp (iφ ₀ (0,0)) + ia ₁ exp (i
(Α ₁ + φ ₀ )) + ia ₂ exp (i (α ₂ + φ
₀ (0,0))) − ｛a ₁ exp (i (α ₁ +
φ ₀ )) {* {a ₂ exp (iα ₂ )}. Here, δexp (iφ ₀ (0,0)) can be ignored at the center spot. Also, ｛a ₁ exp (i (α ₁
+ Φ ₀ )) {* {a ₂ exp (iα ₂ )} is a component scattered by both the amorphous films A1 and A2, and is negligible because it is small.

That is, when the sample 2 is in the irradiation beam, the wave on the observation surface C is ia ₁ exp (i (α ₁ + φ ₀ )) + ia ₂ exp (i
_{(Α 2 + φ 0 (0,0} ))) , and the when the intensity squared ^{_{this, a 1 2 + a 2 2}} + 2a 1 a 2 cos _{[α 1 -α 2 + φ 0 -φ} 0 (0,0) ] (1) Here, (α ₁ −α ₂ ) is the amorphous film A
The intensity is spatially random because it is a random component based on the phase of 1, A2 and is randomly distributed spatially.

Next, intensity on the observation surface C which removed the sample 2 from the in illumination beam, _{^{similarly, a 1 2 + a 2 2}} + 2a 1 a 2 cos (α 1 -α 2) and (2) Become.

Therefore, taking the difference between the intensity (1) with the sample 2 and the intensity (2) without the sample 2, 2a ₁ a ₂ ｛cos [α ₁ −α ₂ + φ ₀ −φ ₀ (0,
0)]-cos (α ₁ −α ₂ )｝ = − 4a ₁ a ₂ sin
{Α ₁ −α ₂ + [φ ₀ −φ ₀ (0,0)] / 2} × si
n {[φ ₀ −φ ₀ (0,0)] / 2}. Since a ₁ and a _{2 are} almost uniform and α ₁ and α ₂ are random, this is because the phase distribution sin of the sample 2 is
{[Φ ₀ −φ ₀ (0,0)] / 2} is a random modulation si
n {α ₁ −α ₂ + [φ ₀ −φ ₀ (0,0)] / 2}, and the phase distribution of the sample 2 is changed to a contour line (interference fringe).
Directly expressed as

[0020] When the sum of the intensities of the case with sample 2 (1) and the strength in the case of the sample 2 without _{(2), 2 (a 1} 2 + a 2 2) + 4a 1 a 2 cos {α 1 −α ₂
+ [Φ ₀ −φ ₀ (0,0)] / 2 {× cos} [φ ₀ −
φ ₀ (0,0)] / 2｝. The phase distribution of sample 2 is cos ｛[φ ₀ −φ
₀ (0,0)] / 2}, and the sensitivity is small, but the phase distribution of the sample 2 can be directly expressed by contour lines by such addition.

Further, the strength with sample 2 (1)
And the intensity (2) without sample 2 yields 2a ₁ a ₂ cos [α ₁ −α ₂ + φ ₀ −φ ₀ (0,
0)] _{× cos (α 1 -α 2)} = 2a 1 2 a 2 2 {cos [2α ₁ -2α ₂ + 2φ ₀ -
2φ ₀ (0,0)] + cos [φ ₀ -φ _{0 (0,}
0)]｝. Also in this case, cos [φ ₀ −φ ₀ (0, 0)]
Represents a contour line of the phase distribution of the sample 2.

The measurement of the intensity distribution on the observation surface with and without the sample 2 may be performed by photoelectric conversion or photographically. The calculation of the difference, the sum or the product may be performed electronically or photographically. In order to perform this operation photographically, it is difficult to calculate the difference. To calculate the sum, once the sample is exposed, the sample is removed, and then exposed again (double exposure) and developed. Often, the product is calculated by
After developing and exposing and developing another film in the same manner when there is no sample, both films may be superimposed and the distribution of transmitted light may be observed.

The case where the Fraunhofer diffraction is established has been described above, but the case where the Fresnel diffraction is also established is similarly applied. Therefore, instead of the arrangement of FIG. 1, the observation may be performed by the arrangement as shown in FIG. That is, in this case, the amorphous films A1 and A2 are conjugated with one electron lens B1 interposed therebetween, and the electron lens B1
When the sample 2 is placed on the back focal plane of the sample and a position conjugate with the sample 2 of another electron lens B2 placed behind the amorphous film A2 is set as the observation plane C, observation is performed in the same manner as in FIG. Good.

The scattering films A1 and A2 may be any as long as they have a random distribution. Here, the meaning of random means that when the distribution is Fourier-transformed, the amplitude is constant and the phase is random. In the case of an electron beam, an amorphous film formed by depositing carbon, germanium, or the like in a medium vacuum relatively meets this requirement and is suitable.

Although the above description has been made on the case of an electron beam whose amplitude division is difficult, the present invention can be similarly applied to other waves such as X-rays, light, and sound waves.

[0026]

As is apparent from the above description, according to the phase information observing method and the phase information observing interference device of the present invention, two scattering films that randomly scatter incident waves are arranged conjugately. A sample is placed between the two scattering films, and a first interference pattern due to the wave passing through both scattering films is detected,
By detecting the second interference pattern in the same detection state with the sample removed and calculating the difference, the sum or the product of the two detected interference patterns, the equiphase fringe of the sample can be directly observed.

The advantages of applying the present invention to an electron beam as compared with the conventional method are that a vacuum region for a reference wave is not required (advantageous in measuring a magnetic field having a continuous distribution).
Direct and real-time observation can be performed (reproduction is unnecessary), and interference fringes can be obtained even with an electron beam source having poor coherence.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining the principle of phase information observation according to the present invention.

FIG. 2 is a diagram for explaining a modified example.

FIG. 3 is a diagram for explaining the principle of electron beam holography using a conventional electronic biprism.

FIG. 4 is a diagram for explaining the principle of electron beam holography by amplitude division using a conventional crystal.

[Explanation of Signs] 1 ... Incident electron beam 2 ... Sample A1, A2 ... Amorphous film B1, B2, B3 ... Electronic lens C ... Observation surface

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H01J 37/26-37/295

Claims (4)

(57) [Claims] 1. A first interference pattern due to waves passing through both scattering films, wherein two scattering films for randomly scattering incident waves are arranged conjugately, a sample is arranged between the two scattering films. Is detected, the second interference pattern is detected in the same detection state where the sample is removed, and the difference between the two detected interference patterns,
A phase information observing method characterized in that phase information of a sample is observed as interference fringes by taking a sum or a product. 2. The phase according to claim 1, wherein the sample arrangement position is a position where a component which goes straight on the incident side scattering film is narrowed down, and both interference pattern detection positions are conjugate positions with the sample arrangement position. Information observation method. 3. An interferometer capable of observing phase information of a sample as interference fringes, two scattering films for randomly scattering incident waves, and one interposed between the two scattering films. A lens system that forms an image of the film on the other scattering film, and an image of a sample in which a component that goes straight through one of the scattering films is disposed at a position narrowed by the lens system or a sub-system thereof, is formed on the observation surface. An interferometer for observing phase information, comprising: a second lens system for performing an operation and a device for recording an interference pattern formed on an observation surface. 4. The interferometer for phase information observation according to claim 3, wherein the incident wave is an electron beam, and the scattering film is made of an amorphous film.